I have 2 30 gallons. one is a livebearer tank, Mollies and Platys with some Corydoras. The other is a heavier planted tank with Mystery Snails, Shrimp and Guppies. I think another one would be Honey or Dwarf Gourami. Or even a school of Danios, or Rasboras. I have a 40 with Kuhli Loaches in it. They would do fine in a 30 I think.